This invention relates to improvements in cathode plates for electro-winning and refining, and in particular to cathode plates for electro-winning and refining zinc, copper, and other metals from solutions by an electrolysis process.
Electrolysis is performed by passing an electric current through an electrolyte, causing migration of positively charged ions to the negative electrode (cathode) and the negatively charged ions to the positive electrode (anode). High purity metals such as zinc and copper can be obtained by electrolysis processes.
As shown in FIGS. 1 and 2, the electro-winning and refining electrolysis is performed in an electrochemical cell 10. The cell consists of anode and cathode plates immersed in an electrolyte solution and an external circuit that permits the flow of electrons from the anode to the cathode.
A cathode (the negative electrode) and the anode (the positive electrode) are immersed in the electrolyte solution, and a direct current (DC) source is connected to the electrodes. This causes both a reduction reaction and an oxidation reaction to occur. Positives ions (such as Zn++ and Cu++) migrate to the negative electrode and are deposited onto the cathode surface in the form of a pure metal sheet (the reduction reaction). Negative ions migrate to the positive electrode and give up an electron and result in generating of gas such as oxygen (oxidation reaction).
It is essential that the electrolyte should be a chemical compound that is dissociated or ionized in an acid solution such as ZnSO4 or CuSO4 containing the metal to be recovered, and be conductive to the electric current.
Once the metal is deposited on the cathode plate by electrolysis, the metal-deposited cathode is transferred to a stripping area by crane. A stripping machine needs stripping knives to initiate the stripping of the recovered metal from the cathode plate. The knives first separate the deposited metal from the plate at the upper boundary of the deposit, and work their way down to the bottom of the deposited metal on the cathode plate to complete the stripping. As shown in FIG. 2, the cathode plate comprises a sheet of aluminum (Al), a head bar 24 welded to the aluminum plate for current transmission to the plate, and two hooks 26 for transferring the plate.
Stripping can be difficult, because the deposited metal is strongly attached at the side edges of the catheters. Recently, plastic ribbons have been placed on the side edges of cathode plates to facilitate stripping. The ribbons secure the space between the deposited metal and the side edges of the cathode plate, promoting easier stripping.
Because the electrolyte level varies during the process, the upper edge of the metal deposited on the cathode plates forms an acute angle along line Dxe2x80x94D in FIG. 2, and shown clearly in FIG. 2a. The irregular top edge of the deposited metal sometimes causes the stripping knives to slip on the top of the metal deposit, requiring that relatively high pressure be applied to the stripping knives that can damage the surface of the aluminum cathode plate.
The stripping process is preferably automated, so the stripping process must proceed smoothly or there will be a reduction in productivity and an increase in manpower.
The present invention relates to an improvement in the construction of cathode plates, to facilitate the stripping of deposited metal. Generally, the cathode plate of the present invention comprises an aluminum sheet or panel, having a header bar, and two hooks. A plastic shield is formed on the upper portion of the cathode plate, just below the head bar, and plastic ribbons are formed along the side edges of the sheet. This plastic has a specified thickness, and the lower edge of the plastic shield slopes toward the surface of the sheet at a specified angle.